1. Field of the Invention
The present invention relates to an image input apparatus for inputting an object image by using a plurality of sensors.
2. Related Background Art
In the field of medical equipment, apparatuses capable of providing high diagnosis efficiency and high precision have been desired. Although X-ray imaging apparatuses using films have been the main trend, demands for processing digital X-ray image data are becoming high. For example, X-rays transmitted through an object is projected upon an X-ray imaging apparatus and displayed on a display device for real time diagnosis.
Digital X-ray image data can be managed by using a recording medium such as a magnetooptical disk. Digital X-ray image data of a patient can be transmitted to a remote site by various communication methods, and the image can be monitored in real time at the remote site.
Diagnosis more precise than conventional can be achieved through image processing of digital X-ray image data. Disadvantages associated with a conventional film type can be solved. Digital X-ray image data is being used not only in the medical field but also in the industrial field. For example, a digital X-ray image input apparatus is used for crystalline analysis of materials, and research in use of an X-ray semiconductor-exposure system for manufacturing and monitoring semiconductor devices with ultra fine patterns on a semiconductor wafer is also being done.
In place of an X-ray imaging apparatus using films, an image input apparatus using a two-dimensional CCD solid state image sensing device has been developed to attain digital X-ray image data processing.
A flat panel sensor has been developed which has a large substrate on which photoelectric conversion element layer made of amorphous silicon (a-Si) hydride are formed. An X-ray imaging apparatus using such a flat panel sensor is also under development.
Since a-Si can be used as material of both photoelectric conversion elements and thin film transistors (TFT), photoelectric conversion elements and TFTs can be easily formed on the same substrate. A large area sensor of an equal magnification type using a combination of a scintillator, TFTs and photoelectric conversion elements has been studied.
An X-ray image input apparatus of a flat panel type has been desired which has a large image area and a high sensitivity and which is compact, light, and compatible with high speed moving images. It is desired that the pixel pitch of such an X-ray image input apparatus is 100 xcexcm or smaller and that the effective image area of photoelectric conversion pixels is at least 40 cmxc3x9740 cm for sensing an image of a human chest.
Problems associated with conventional X-ray image input apparatuses of a large screen type are given in the following.
A CCD solid image sensing device having a size as large as a human body is impossible at present. A currently available size of a CCD sensor is 2 cm square. Therefore, in order to input a large area image to the CCD solid image sensing device, it is necessary to reduce the size of a fluorescent image, i.e., X-ray image, from a scintillator by using an optical reduction system and to focus the image upon a CCD light reception surface.
With a CCD sensor using an optical reduction system, however, an S/N ratio of an image is lowered by two to three digits because the image passes through a lens, although it depends on a reduction factor. Therefore, such a CCD sensor is not suitable for use with medical apparatuses which require high image gradation.
An X-ray imaging apparatus having a plurality of combinations of an optical reduction system and a CCD solid state image sensing device has been proposed which can provide a large image area while retaining a high S/N ratio. The sensitivity is, however, inferior to an equal magnification type, and the size of the X-ray imaging apparatus becomes large because lens systems are incorporated.
A CCD solid state image sensing device made of single crystal silicon and electronic components used as its peripheral circuit are likely to be affected by X-rays, and thus X-ray shielding is required.
A CCD solid state image sensing apparatus such as shown in FIG. 1 is known which is made of a combination of a CCD sensor, a fiber plate of an equal magnification optical system and a scintillator. This CCD sensor has: a pixel area 82 made of four modules; a non-pixel area 83 in which vertical and horizontal scan circuits, an image processing circuit and the like are formed; and an electrical mounting area 84 around the non-pixel area in which lead connectors and the like are mounted. However, with this structure, the maximum number of CCD modules is only four and a large area is hard to be realized.
In order to make a larger area, U.S. Pat. No. 5,834,782 proposes an image input apparatus shown in FIGS. 2A and 2B. FIG. 2A is a perspective view of the apparatus and FIG. 2B is a plan view thereof as viewed along an X-ray incidence direction. A plurality of area sensors 91 of CCD sensors or CMOS sensors are arranged with facing incident X-rays and on different steps so as to overlap with each other in a peripheral area. X-rays become incident and are introduced via a fiber array to the pixel area 94. Each area sensor 91 has the pixel area 94 and a signal output area (non-pixel area) 93 which is formed one side of the sensor. A fiber array 92 has steps on which the area sensors 91 are arranged. If the number of steps of the fiber array 92 is increased, a large number of area sensors or modules can be used theoretically. With this structure, however, a read/scan circuit for the area sensor is required to be formed on one side of the sensor. Therefore, electrical mounting areas (non-pixel areas) are concentrated on two sides among four sides of the panel, and the other two sides are not used effectively. It is therefore difficult to form a compact image input apparatus. This becomes a critical issue when a number of area sensors of a small size are used.
If a flat panel type is used, a large image area of an equal magnification without an optical reduction system becomes possible. An S/N ratio is better than a CCD solid state image sensing device with an optical reduction system.
Since an optical reduction system is not used, the apparatus can be made more compact and is suitable for use in a hospital or medical examination vehicle which does not have a large space.
Although the flat panel made of four modules such as shown in FIG. 1 is widely used, the number of modules is four at a maximum. It is difficult to use modules more than four to form a panel of large area. With this structure, coupling areas between modules are inevitably positioned in the central area of the panel. This central area is often used to obtain image data. If this coupling areas form any image defects, these defects become visually conspicuous and the image quality is degraded considerably.
It is difficult to realize higher sensitivity and higher operation speed of a flat panel using a-Si TFTs and a-Si photoelectric conversion elements, because of restrictions specific to a-Si semiconductor. A flat panel having high sensitivity and high operation speed and compatible with moving images has therefore been considered difficult to manufacture.
It is an object of the invention to properly dispose a plurality of sensors so that an image of high quality can be obtained.
In order to achieve the above object, aspect of the present invention provides an image input apparatus having a plurality of sensors each including a pixel area in which a plurality of pixels are arranged, the image input apparatus comprising: a first group including one or a plurality of pixel areas; and a second group including a plurality of pixel areas arranged adjacently to each other surrounding one or the plurality of pixel areas of the first group, as viewed along an image input direction, wherein the plurality of pixel areas of the second group are arranged nearer to an image input surface than one or the plurality of pixel areas of the first group.
Another aspect of the invention provides an image input apparatus having a plurality of sensors each including a pixel area in which a plurality of pixels are arranged in a square shape or a rectangle shape, the image input apparatus comprising: a first group including one or a plurality of pixel areas; and a second group including a plurality of pixel areas arranged adjacent to one or the plurality of pixel areas of the first group along four sides of the first group and along four diagonal directions, as viewed along an image input direction, wherein the second group is arranged nearer to an image input surface than the first group.
Other objects and features of the present invention will become apparent from the following detailed description of embodiments when read in conjunction with the accompanying drawings.